Casting device and associated method for investment casting with improved mechanical
properties

ABSTRACT

The invention describes a method of casting a metal comprising the following steps: fabricating a pattern from wax or plastic having the geometry to generate a desired object, fabricating an investment mold from the wax, placing the mold in an open pressure vessel, filling the investment mold with a molten metal alloy, immediately thereafter closing and pressure sealing the pressure vessel, pressurizing the sealed pressure vessel with an inert gas for a predetermined measured time, depressurizing the sealed pressure vessel, opening the pressure vessel and removing the metal filled investment mold, and extracting the desired object from the investment mold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/124,015 filed Dec. 6, 2014, which hereby isincorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention is directed generally to manufacturing metalobjects and more specifically to a method to investment cast metalobjects.

BACKGROUND

Investment casting is a metal casting process by which a duplicate metalobject is cast from a pattern which is destroyed in the process ofmaking the mold or casting. Investment casting is an industrial processbased on and also called lost wax casting. The term “investment casting”can also refer to an object produced via the investment casting process.From 5,000 years ago when beeswax formed the pattern to today'shigh-technology waxes, the castings allow the production of componentswith excellent surface finish, high dimensional accuracy, and extremeintricacy in a variety of metals and high-performance alloys. Investmentcastings are produced in specialized factories commonly referred to asfoundries. Investment casting is generally more expensive per unit thandie casting or sand casting. Investment casting can produce complicatedshapes that would be difficult or impossible with other methods andrequires little surface finishing and only minor post-machining. It isused to produce common everyday metal objects as well as intricateaerospace and military components. Cast objects can be made of the modelitself, the direct method; or of a copy of a model, the indirect method.

A master pattern or the desired object is fabricated, although this stepis often replaced with a digital CAD model. A negative cavity mold ismade of the master pattern or from the CAD model. Wax patterns arecreated from the negative cavity mold by injecting heated liquid waxinto the chilled negative cavity mold. The wax pattern is then removedfrom the negative cavity mold, or alternately in lower volumeapplications, a 3D printed plastic pattern from a CAD model is used.Depending on the application, multiple wax patterns may be created sothat they can all be cast at once. The multiple patterns are attached toa wax sprue, with the result as a wax pattern cluster, or tree. Theceramic mold, known as the investment mold, is produced by threerepeating steps: coating, stuccoing, and hardening. The first stepinvolves dipping the assembled and prepared cluster into a slurry offine refractory material and then letting any excess drain off so auniform surface is produced. This fine material is used first to give asmooth surface finish and reproduce fine details. In the second step,the cluster is stuccoed with a ceramic particle by dipping it into afluidized bed, placing it in a rainfall-sander, or by applying by hand.Finally, the coating is allowed to harden. These steps are repeateduntil the investment mold is the required thickness. Another method isto secure the pattern and tree in a container and pour a slurry aroundit which hardens for the full-mold or solid-mold variant of the process.The investment mold is then allowed to completely dry. It is then placedin a favorable position, typically upside down, to drain and is placedin a furnace or autoclave to melt out and/or vaporize the wax. Theinvestment mold is then subjected to a burnout and preheat to remove anymoisture and residual wax and to sinter the mold. The investment mold isthen placed cup-upwards and filled with molten metal. The cast part isallowed to cool and fully solidify. Once solidified, the investment moldis removed by vibration, water blast, or a chemical process. The sprueis trimmed away leaving the final desired object(s). The molding processproceeds generally along the following 10 steps:

-   -   Step #1: Fabricate a master pattern or create a CAD model.    -   Step #2: A negative cavity mold is made of the master pattern or        CAD model.    -   Step #3: Produce the wax patterns from the negative cavity mold        or 3D printed plastic pattern.    -   Step#4: Assemble the wax patterns into a pattern cluster, or        tree.    -   Step #5: The ceramic mold, known as the Investment mold, is        produced by repeating the steps: coating, stuccoing, and        hardening.    -   Step #6: Turn the investment mold upside down and place in a        furnace or autoclave and melt out and/or vaporize the wax.    -   Step #7: Burnout of the investment mold to remove any moisture        and residual wax and sinter the mold.    -   Step #8: Place the investment mold pouring cup upwards, and fill        the investment mold with molten metal.    -   Step #9: Allow the metal to cool and fully solidify.    -   Step #10: Break away the investment mold and trim the cast        object.

SUMMARY OF THE INVENTION

The present invention is directed generally to manufacturing cast metalobjects and more specifically to a method and device to investment castmetal objects.

One embodiment of the present invention describes a method of casting ametal alloy comprising the following steps: fabricating a pattern fromwax or plastic having the appropriate geometry to generate a desiredobject to be cast, fabricating an investment mold from the wax orplastic, placing the investment mold in an open pressure vessel, fillingthe investment mold with a molten metal alloy, immediately thereafterclosing and pressure sealing the pressure vessel, pressurizing thesealed pressure vessel with an inert gas for a predetermined measuredtime said predetermined measured time sufficient for the molten metal tocool and solidify, depressurizing the sealed pressure vessel, openingthe pressure vessel and removing the metal filled investment mold, andextracting the desired object from the investment mold.

Another embodiment of the present invention describes a method ofcasting a metal alloy comprising the following steps: fabricating apattern from wax or plastic having the appropriate geometry to generatea desired object to be cast, fabricating an investment mold from the waxor plastic, placing the investment mold in an open pressure vessel,filling the investment mold with a molten metal alloy, immediatelythereafter closing and pressure sealing the pressure vessel,pressurizing the sealed pressure vessel with an inert gas for apredetermined measured time said predetermined measured time sufficientfor the molten metal to cool and solidify, withdrawing the inert gasfrom the sealed pressure vessel and transferring said inert gas into areusable storage device thereby depressurizing the sealed pressurevessel, opening the pressure vessel and removing the metal filledinvestment mold, and extracting the desired object from the investmentmold.

Another embodiment of the present invention describes a method ofcasting a metal alloy comprising the following steps: fabricating apattern from wax or plastic having the appropriate geometry to generatea desired object to be cast, fabricating an investment mold from the waxor plastic, filling the investment mold with a molten metal alloy,placing the investment mold in an open pressure vessel, immediatelythereafter closing and pressure sealing the pressure vessel,pressurizing the sealed pressure vessel with an inert gas for apredetermined measured time said predetermined measured time sufficientfor the molten metal to cool and solidify, withdrawing the inert gasfrom the sealed pressure vessel and transferring said inert gas into areusable storage device thereby depressurizing the sealed pressurevessel, opening the pressure vessel and removing the metal filledinvestment mold, and extracting the desired object from the investmentmold.

Another embodiment of the present invention describes a method ofcasting a metal alloy comprising the following steps: fabricating apattern from wax or plastic having the appropriate geometry to generatea desired object to be cast, fabricating an investment mold from the waxor plastic, placing the investment mold in an open pressure vessel,filling the investment mold with a molten metal alloy, packing loosesand around the metal filled investment mold and held by a container,immediately thereafter closing and pressure sealing the pressure vessel,pressurizing the sealed pressure vessel with an inert gas for apredetermined measured time said predetermined measured time sufficientfor the molten metal to cool and solidify, withdrawing the inert gasfrom the sealed pressure vessel and transferring said inert gas into areusable storage device thereby depressurizing the sealed pressurevessel, opening the pressure vessel and removing the metal filledinvestment mold, and extracting the desired object from the investmentmold.

Another embodiment of the present invention describes a device forcasting a metal alloy comprising the following elements: a pressurevessel head, a pressure vessel base incorporating a surface to support asand casting mold, a vertical travel guide in mechanical communicationwith the pressure vessel head and the pressure vessel base, saidpressure vessel head and pressure vessel base incorporating interlockingmembers capable of forming a pressure seal when interlocked, and anactuator capable of engaging the interlocking members thereby forming apressure seal when the pressure vessel head is in mechanicalcommunication with the pressure vessel base.

The above summary of the present invention is not intended to describeeach illustrated embodiment or every implementation of the presentinvention. The figures and the detailed description which follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 shows a schematic representation of a pressure vessel shown inthe open configuration. The pressure vessel may be comprised of apressure vessel head, a vertical travel guide, and a pressure vesselbase which is designed to form a pressure seal when in mechanicalcommunication with the pressure vessel head.

FIG. 2 shows the pressure vessel depicted in FIG. 1 incorporating aninvestment mold placed on the pressure vessel base.

FIG. 3 shows the pressure vessel depicted in FIG. 1 in the closed andunlocked, i.e. non-pressurized, configuration.

FIG. 4 shows the pressure vessel depicted in FIG. 1 in the closed andpressurized configuration while in airway communication with an externalsource of a pressurized inert gas.

FIG. 5 shows the pressure vessel depicted in FIG. 1 incorporating aninvestment mold with loose sand packed around it held by a container andplaced on the pressure vessel base.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention is directed generally to manufacturing metalobjects and more specifically to a device and method to investment castmetal objects. One embodiment of the present invention is depictedschematically in FIGS. 1 through 5, highlighting the apparatus topressurize an encased metal filled investment mold with an inert gas.

FIG. 1 depicts a pressure vessel 10 shown in the open configuration. Thepressure vessel 10 may be comprised of a pressure vessel head 12, avertical travel guide 14, and a pressure vessel base 16 which isdesigned to form a pressure seal when in mechanical communication withthe pressure vessel head 12.

In one embodiment of the present invention, an investment mold 20 (seeFIG. 2) having the appropriate internal geometry to generate a desiredobject to be cast may be placed on a planar substrate 18 which is partof the pressure vessel base 16. Once in place, the investment mold 20may be filled with a molten metal, preferably an aluminum alloy.Immediately after filling the investment mold 20 with molten metal, thepressure vessel head 12 may be lowered and placed in mechanicalcommunication with the pressure vessel base 16. In placing the pressurevessel head 12 in mechanical communication with the pressure vessel base16, care may be taken to align the male interlocking elements 22Aadhered to the bottom of the pressure vessel head 12 with the femalecounterpart interlocking elements 22B adhered to the pressure vesselbase 16 as shown in FIG. 3. Once properly aligned, a linear actuator 24attached to the pressure vessel base 16 may be energized which in turnmay interlock the male and female locking elements thereby pressuresealing the pressure vessel.

Once the pressure seal has been established, an external source of aninert pressurized gas, preferably helium, may be inserted into thepressure sealed vessel by way of a valve 26 incorporated into the wallof the pressure vessel base 16 as depicted in FIG. 4. In one embodimentof the present invention, the inert gas may pressurize the sealed vesselin the range of 50 to 180 pounds per square inch. The sealed, inert gaspressurized vessel may remain pressurized for a predetermined timecommensurate with the size of the investment casting mold and the volumeof molten metal encased therein.

In one embodiment of the present invention, the investment mold 20 maybe encased within loose sand 28 and confined within container 30, asdepicted in FIG. 5.

In a preferred embodiment of the present invention, the pressure vesseland the external source of inert gas may be configured to reclaim andpurify for later reuse the inert gas used previously in the process ofpressurizing the pressure vessel as described above.

The present invention should not be considered limited to the particularexamples described above, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes as well as numerousstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art of casting metal objects.For example, the invention anticipates other geometrical configurationsfor the pressure vessel including but not limited to a horizontal designin contrast to the vertical configuration outlined in the abovedescription. Also, the present invention anticipates that the time forthe molten aluminum to cool and fully solidify while still encasedwithin the pressure chamber may depend upon the volume of moltenaluminum poured, and in many cases, the ratio of volume-to-surface areaof the encased aluminum, and one of ordinary skill in the art may makethat determination theoretically or by experimentation. The followingclaims are intended to cover such modifications and devices.

I claim:
 1. A method of casting a metal alloy comprising the followingsteps: fabricating a pattern from wax or plastic having the appropriategeometry to generate a desired object to be cast; placing the investmentmold in an open pressure vessel; filling the investment mold with amolten metal alloy; immediately thereafter closing and pressure sealingthe pressure vessel; pressurizing the sealed pressure vessel with aninert gas for a predetermined measured time; said predetermined measuredtime sufficient for the molten metal to cool and solidify;depressurizing the sealed pressure vessel; opening the pressure vesseland removing the metal filled investment mold; and extracting thedesired object from the investment mold.
 2. The method of claim 1wherein the investment mold may be comprised of aluminosilicate stucco,fused silica, crystalline silica, colloidal silica, zircon, alumina,zirconium oxide, silica sand (SiO₂), chromite sand (FeCr₂O), zircon sand(ZrSiO₄), staurolite, graphite, organic and inorganic binders consistingof latex polymers, water-soluble polymers, and combinations thereof. 3.The method of claim 1 wherein the inert gas may be helium, argon,nitrogen, oxygen or combinations thereof.
 4. The device of claim 1wherein the sealed pressure vessel is pressurized to a value in therange of 50 to 180 pounds per square inch with the inert gas.
 5. Amethod of casting a metal alloy comprising the following steps:fabricating a pattern from wax or plastic having the appropriategeometry to generate a desired object to be cast; placing the investmentmold in an open pressure vessel; filling the investment mold with amolten metal alloy; immediately thereafter closing and pressure sealingthe pressure vessel; pressurizing the sealed pressure vessel with aninert gas for a predetermined measured time; said predetermined measuredtime sufficient for the molten metal to cool and solidify; withdrawingthe inert gas from the sealed pressure vessel and transferring saidinert gas into a reusable storage device thereby depressurizing thesealed pressure vessel; opening the pressure vessel and removing themetal filled investment mold; and extracting the desired object from theinvestment mold,
 6. The method of claim 5 wherein withdrawing the inertgas from the sealed pressure vessel may include filtering and separatingunwanted gaseous compounds prior to transferring the said inert gas intoa reusable storage device.
 7. A method of casting a metal alloycomprising the following steps: fabricating a pattern from wax orplastic having the appropriate geometry to generate a desired object tobe cast; filling the investment mold with a molten metal alloy; placingthe investment mold in an open pressure vessel; immediately thereafterclosing and pressure sealing the pressure vessel; pressurizing thesealed pressure vessel with an inert gas for a predetermined measuredtime; said predetermined measured time sufficient for the molten metalto cool and solidify; withdrawing the inert gas from the sealed pressurevessel and transferring said inert gas into a reusable storage devicethereby depressurizing the sealed pressure vessel; opening the pressurevessel and removing the metal filled investment mold; and extracting thedesired object from the investment mold.
 8. The method of claim 7wherein withdrawing the inert gas from the sealed pressure vessel mayinclude filtering and separating unwanted gaseous compounds prior totransferring the said inert gas into a reusable storage device.
 9. Amethod of casting a metal alloy comprising the following steps:fabricating a pattern from wax or plastic having the appropriategeometry to generate a desired object to be cast; placing the investmentmold in an open pressure vessel; filling the investment mold with amolten metal alloy; encasing the investment mold in sand; immediatelythereafter closing and pressure sealing the pressure vessel;pressurizing the sealed pressure vessel with an inert gas for apredetermined measured time; said predetermined measured time sufficientfor the molten metal to cool and solidify; withdrawing the inert gasfrom the sealed pressure vessel and transferring said inert gas into areusable storage device thereby depressurizing the sealed pressurevessel; opening the pressure vessel and removing the metal filledinvestment mold; and extracting the desired object from the investmentmold.
 10. The method of claim 9 wherein withdrawing the inert gas fromthe sealed pressure vessel may include filtering and separating unwantedgaseous compounds prior to transferring the said inert gas into areusable storage device.
 11. A device for casting a metal alloycomprising the following elements: a pressure vessel head; a pressurevessel base incorporating a surface to support an investment mold; avertical travel guide in mechanical communication with the pressurevessel head and the pressure vessel base; said pressure vessel head andpressure vessel base incorporating interlocking members capable offorming a pressure seal when interlocked; and an actuator capable ofengaging the interlocking members thereby forming a pressure seal whenthe pressure vessel head is in mechanical communication with thepressure vessel base.
 12. The device of claim 11 wherein the pressurevessel base incorporates a unidirectional valve device to receive aninert gas from an external source.
 13. The device of claim 11 whereinthe pressure vessel base incorporates a bidirectional valve device withthe means to receive an inert gas from an external source and exhaustsaid inert gas into an external source for later reuse.